Saturday, 15 July 2006

Rotation and Tillage Affects on Soil Organic Carbon and Management of No-Till Acid Soils.

Chad Godsey, Gary Pierzynski, David Mengel, and Ray Lamond. Kansas State Univ, 2004 Throckmorton PSC, Dept of Agronomy, Manhattan, KS 66506-5501

Recent attention has focused on management of acid soils in No-Till (NT) due to the limited movement of surface-applied lime in these systems. Interactions of exchangeable Al and Organic Carbon (OC) have been recognized for many years, but limited data exists considering how these interactions should affect management decisions for NT soils. The objectives of this experiment were to 1) identify effects of rotation and tillage on soil pH and soil OC content, 2) determine the influence of these changes on KCl and CuCl2 extractable-Al, and 3) determine how changes in OC may affect management decisions regarding soil acidity. Soil samples were collected to a depth of 15 cm, in 2.5- cm increments, from a long-term rotation and tillage study near Manhattan, KS. Main plot treatments included continuous wheat [Triticum aestivum (L.) sp. aestivum], soybean [Glycine max (L) Merr.], grain sorghum (Sorghum bicolor (L.) Moench], and rotations of soybean-sorghum or wheat-soybean. Sub-plot treatments were NT and conventional till (CT). Soil pH and OC concentrations were greatly influenced by rotation and tillage. Organic C concentrations were on average 2.3 g/kg greater with NT than CT in the surface 15 cm of soil. Potassium chloride and CuCl2 extractable-Al increased exponentially with decreasing soil pH (Figure1). CuCl2 extractable-Al values were on average 33% greater than KCl extractable-Al levels. When using a regression model to predict the difference between CuCl2 extractable and KCl extractable-Al (assumed to be Al associated with OC), inclusion of OC explained only 4% greater variability compared with inclusion of only soil pH in the model. Changes in OC concentrations in the surface 7.5 cm of soil often observed after reducing tillage would likely not alleviate Al toxicity if pH became very acidic (pH<5). Therefore, pH critical values for liming acid soils in NT production systems should not be adjusted based on tillage practices.

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